Letter to the editor concerning "Contrast sensitivity function with soft contact lens wear".

Dear Editor,

This is in reference to the article titled: Contrast sensitivity function with soft contact lens wear by the authors Kishor Sapkota Sandra Franco and Madalena Lira published in the current issue of the Journal of Optometry.

Contrast sensitivity has become far more integral part of standard practice over the past number of years especially since the emphasis on improving amblyopia, in sports, vision post refractive surgeries to well beyond 6/6 and the ever-higher demands of our patients for the best possible vision.2, 3 Information which optical devices offer us that is immediately clinically implementable and very helpful.

There were a few things the readers felt worthy of note, with your permission.

The results comparing contrast sensitivity function (CSF) between contact lenses and spectacles in this study where the patients used their habitual spectacles were a little troublesome. In addition to the authors’ reporting that the prescription was possibly not the full refraction, the status of the lenses in their glasses has the potential to affect the results. It feels important to equalize and optimize optical qualities of the lenses as far as material, anti-reflective coatings (or absence thereof), integrity of coatings (and no scratches), an aspheric versus spheric optical design before testing CSF.4, 5

Contrast sensitivity is influenced by the tear film both quality and quantity. A Schirmer’s test alone yields very little information about the consistency and quality (lipid content and quality, debris).6, 7

All the monthly lens wearers used the Opti Free multi-purpose solution (MPS) as a disinfectant and storage system. It would have been exciting to see a comparison with patients using an H2O2 system, whether the type of solution or protein buildup may have yielded different results at the end of the month of wear. There is quite a bit of data showing MPS can be absorbed in the lens as well as cause comfort issues.8, 9

It was interesting that the researchers chose to check the patients after three months when the patients used fresh lenses monthly. Testing at the end of the first month when lenses are about to be disposed and compared with the fresher daily lenses would have been just as effective.

While the same technology was used to measure the contrast sensitivity at each examination and under the same environmental circumstances, it felt that assessing the Modulation Transfer Function (MTF) of each lens, an objective parameter, would have supported the subsequently drawn data.

Conflict of interest

The authors have no conflicts of interest to declare.

Financial support

The authors of this letter did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.